Process of winning elemental phosphorus



Oct. 6, 1959 s. TOUR 2,907,637

PROCESS OF WINNING ELEMENTAL PHOSPHORUS Filed 001;. 5, 1955 2Sheets-Sheet 1 5AM TOUR.

ATTORNEY Oct. 6, 1959 s. TOUR 2,907,637

PROCESS OF WINNING ELEMENTAL PHOSPHORUS Filed Oct. 5, 1955 2Sheets-Sheet 2 IN VENTOR 2- 5/1/14 TOUR ATTORNEY United States PatentirRocEs's 0F WINNING ELEMENTAL rnosrnorws Application October 5, 1955,Serial No. 538,597

12 Claims. (Cl. 23-423 This invention is a new and useful process ofwinning Telemental phosphorous from oxygenated ores containing the same,such as the so-called phosphate rock. The "invention is an improvementon the method described and claimed in application of Louis Burgess,Serial No. 530,507, filed August 25, 1955, the said application and theinstant application being assigned to the identical assignee. Thisinvention will be fully understood from following description read inconjunction with the drawings in which:

Fig. l is a diagrammatic vertical section thru apparatus in which theinvention may be practiced;

Fig. 2 is a detailed vertical section through one elementbf theapparatus shown in Fig. 1;

Fig. 3 is a horizontal section through the plane indicated by 3-3 inFig. 2; and

Fig. 4 is a horizontal section through the plane indicated by4-4 in Fig.2.

i The elements of the process for the recovery of elemental phosphorusdescribed in said application, Serial No. 530,507, are as follows:

(a) The formation of a coke throughout which the particles of the oreare disseminated in a supporting structure of carbon and in which thecarbon is in excess of that consumable by reduction of the ore and otherreducible substances present;

(b) Heating the coke so formed out of direct confact with combustiongases to a temperature at which the ore is reduced by carbon therebyproducing elementa'l phosphorus and carbon monoxide in vapor phase,conducting away the vapor phase and condensing the phosphorus;

(c) Removing the residue of excess carbon and inorganic oxides froin theheating zone in solid form.

The substantially complete liberation of the elemental phosphorus instep (b) and the removal of the residuein solid form, step (c), are madepossible by the preliminary step (a i.e., the formation of a coke inwhich the particles are disseminated and in which the carbon is inexcess. The combined effect of the coke structure and the excess carbonin this coke structure is to hold the oxide particles apart up to thepoint of complete reduction and at this point, to provide sufficientresidual carbon to hold the residual oxide particles apart and therebyprevent sintering. In the preferred embodiment, suflicient excess carbonis incorporated to maintain the physical form of the individual massesof which the charge is composed.

In one method of generating the desired coke structure, the oxide ismixed with sufiicient of a substance selected from the tars, pitches,and asphalts (including the oxidized asphalts), to occupy the spacesbetween the oxide particles. Sufficient coke breeze, anthracite2,907,637 Patented Oct. 6, 1959 or bituminous coal of about the sameparticle size as the oxide particles, is also incorporated in amountsufficient to provide the requisite carbonzoxide ratio. In anothermethod, the oxide and bituminous coal, are ground together in a state ofextreme fineness for a period of several hours. The grinding iscontinued until the individual particles of oxide and coal are no longerseparately distinguishable and the coal has acquired the property offlowing under extreme pressure. At this stage, the entire mix isbriquetted by the application of pressures of the order of at least tentons per square mc In either method, the coke-forming substance isconverted into coke by raising the temperature progressively through therange of pyrolysis, i.e., about 350-1000 C., until pyrolysis issubstantially complete. With cokeforming substances that become fluidbelow the temperature of pyrolysis, this heating is carried out inapparatus in which the mix is supported in a quiescent state, such as acoke oven or broad oven. With those coke-forming substances which becomeonly plastic and not freely fluid up to the temperature of pyrolysis,the carbonization may becarried out in a vertical retort with top feedand bottom discharge.

Any of the coke-forming substances mentioned may, with suflicientlyrigorous preliminary treatment, be converted into forms that become onlyplastic and not free ly fluid up to the temperature of pyrolysis. Thosepreeminently suited for this purpose are, however, the coal tar pitchesof about C. or higher melting point, as determined by the cube in airmethod and the bituminous coals processed in the manner hereinabovedescribed. It is to this embodiment of the invention described in saidapplication, Serial No. 530,507, that my improvement is directed.

Referring to the drawings, 1 designates a retort of the vertical type,with provision for top feed and bottom discharge. By reference to Fig. 2which shows details of construction, heating zone 2 is bounded bytransverse walls 3 and 4 and end walls 5 and 6 (Figs. 3 and 4). Theseare of refractory heat-conducting material, such as fused alumina orbonded silicon carbide.

Wall 4 is heated by the application of combustion gases to surface 7thereof. For this purpose, burner 8 is provided which may be suppliedwith air and gas through the valved pipes 9 and 10 respectively. Burner8 discharges into combustion space 11 defined by the refractory panels12, 13 and 14. From the combustion space, the products of combustionmove upwardly through duct 15 defined by the refractory Walls 4, 5, 6and 16. They follow a sinuous path over the staggered horizontal bafiles17 as indicated by arrows 18, eventually passing out through the stack19, by which they are discharged.

Transverse wall 3 is heated by the application of combustion gases tosurface 20 thereof. For this purpose, burner 21 is provided which may besupplied with air and gas through valved pipes 22 and 23. The burnerdischarges into combustion space 24 defined by the refractory panels 25,26 and 27. From the combustion space 24, the products of combustion moveupwardly through duct 28 defined by the refractory walls 3, 5, 6 and 29.They follow a sinuous path over staggered baffles 30 as indicated byarrows 31 passing off through the stack 32 by which they are discharged.

Material to be supplied to heating zone 2 is dumped end 38 of heatingzone 2 by means of turnable grate bars 39. The grate bars are rotatedpreferably continuously, by any suitable means, not shown. Materialdischarged by grate bars 39 drops into space 41 from which it may becontinuously or intermittently removed .by the operation of wormconveyor 42. A carrier gas may be introduced into space 41 throughvalved pipe 43. ,n Provision is made for the take-01f of gases fromadjacent the upper part of heating zone 2 through the horizontal ducts44 and 45 (Figs. 2 and 3) discharging intothe main 46 controlled byvalve 47. Provision is also made for the take-offof gases from amid-point of heating zone 2 through the horizontal ducts 48 and 49(Figs. 2 and 4) discharging into the main 50 controlled by valve 51.Main 46 is provided with pressure gauge 52 by means of which thepressure obtaining at this point is indicated. Gases passing otf throughthe main 46 are discharged into the quench tank 53. A liquid such astar, may be supplied to the upper end of tank 53 through valved pipe 54.This liquid is restrained by transverse perforated plate 55 from whichit is discharged downwardly in a large number of small streams. Thisliquid, together with any material condensed out of the gases enteringthrough main 46, accumulates in base 56 of tank 53 up to the levelindicated by line 57. Any excess over this may be continuously withdrawnthrough valved overflow pipe 58 passing through the cooler 59 in whichit passes downwardly through pipes 60 carried in headers 61 and 62. Aliquid may be passed into the space between headers 61 and 62 throughpipe 63 passing .off through pipe 64. From cooler 59, the liquidintroduced through valved pipe 58 is diverted to storage through valvedpipe 651. From tank 53, the gases supplied through'main 46, less anyconstituents which'may have been condensed in the tank 53, pass offthrough valved pipe 71 to pump 72 by which they are supplied to themid-section of rectifying column 73. This column is spanned by a numberof horizontal trays 74 equipped with bell caps and overflow pipes, notshown, for the purpose of dispersing any ascending vapor into the layerof liquid carried by each such tray. It is also equipped with a reboilercoil 75 in the base 76 and with a valved overflow pipe 77 by whichliquid accumulating in'the base over that necessary to maintain thelevel indicated by line 78, may be Withdrawm From the upper end 81 ofthe rectifying column 73 gases are conducted away through pipe 82communieating with condenser 83. In condenser 83, the gases movedownwardly through tubes 34 carried in headers 85 and 86. Provision ismade for cooling the gases in their passage through tubes 84 by theintroduction of a coolant, such as water, through valved pipe 87 to thespace between headers 85 and 86, passing off through valved pipe 88.Condensate together with uncondensed gas passing oil from condenser 83moves downwardly through pipe 89 into the receiving tank 90. Any excessof condensate over that necessary to maintain the liquid level indicatedby line 91 is continuously withdrawn through pipe 92. A part of this isrecycled through valved pipe 93 by means of pump 94 discharging throughpipe 95 into the upper end 81 of column 73, to serve as reflux in column73. The balance is continuously withdrawn to storage through valved pipe96. Bottoms accumulating in the lower end 76 of rectifying column 73 maybe continuously withdrawn to storage through valved pipe 77. Uncon 4densed gas is withdrawn from tank 90 through valved pipe 97. Provisionis made for the ascertainment of pressures obtaining in the heating zoneby means of a number of pressure gauges, such as 101-106, spacedvertically along, and communicating with, the interior of heating zone2.

Provision is also made for the ascertainment of temperatures obtainingin the heating zone by means of a number of temperature responsivedevices such as shielded thermocouples 107-112 spaced vertically alongtransverse wall 35'.

In the operation of the apparatus described, I first compound a suitablecharge. One charge which I may use is compounded of the followingmaterials: phosphate rock analyzing about 70% tricalcium phosphate orits equivalent in P 0 content, roughly two-thirds through 100rnesh androughly 50% through 200 mesh; silica and coke breeze of roughly the sameparticle size as the phosphaterock; coal tar pitch M.P. 100 C. orhigher, as determined bythe cube in air method, coking value at least40%.

These materials should be mixed in the following proportions:

Parts Phosphate ro 360 Silica 120 Coke breeze Coal tar pitch PartsPhosphate ro 360 Silica Bituminous coal The'mix is ball-milled togetherfor a period of at least 12 hours and until the coal has developed theproperty of flowing under relatively higher pressures. At this point theentire charge is briquetted under a pressure of. about 15 tons persquare inch. The briquettes so formed are strong and dense and maytherefore be charged into the heating zone up to the level indicated byline 37, through the hoppers 33 and 35, by operation of hell valves 34and 36. When this has been done, a carrier gas, such as carbon monoxide,is introduced through valved pipe 43 into base 41 of retort 1, at such arate as to maintain positive pressure in the base, and the burners 8 and21 are started in operation. During this stage valve 51 in main 50 isclosed, and as soon as the temperature of pyrolysis is reached andthereafter the vapors produced are taken ofl through main 46 into quenchtank 53, in

which the heavier hydrocarbons are condensed by contact with incomingcoal tar from 54, and the residual hydrocarbons, principally aromatics,are taken over into rectifying column 73. In column 73, by adjustment ofthe amount of reflux returned through line 95 and the amount of heatsupplied through reboiler coil 75, these residual hydrocarbons are splitinto two cuts, i.e., heavier aromatics taken oif from the base of thecolumn through the valved pipe 77 and a lighter overhead consistingprincipally of benzol and toluol, which is taken oil? through valvedpipe 82. Uncondensed gas is taken off through valved pipe 97.

Whenever a temperature of about 1000 C. is reached in the base 38 of theheating zone, the valve 51 in main 50 is partly opened and thephosphorous vapor, together with the carbon monoxide simultaneouslyproduced by reduction, are: conducted away through main 50 to suitablecondensers (not shown) At the same time, flow through main 46 iscontrolled by means of valve 71 and/or 11am ratewhich will carry theheavier products oflpyrolysis overhead through main 46 andtherebyprevent them from co-mingling with and contaminating thephosphorus simultaneously produced. One way of establishing thisadjustment is to make provision for a continuous sampling of thephosphorus coming off through main 50 and to maintain such a flowthrough main 46, by means of pump 72, as is necessary to insure thatthis phosphorus will not show tar contamination.

Another way is to maintain such a rate of fiow by means of the valve inpipe 71 and/ or by means of pump 72 that the maximum pressure in thatpart of the heating zone above outlets 48 and 49 occurs at the 700-800C. (preferably about 750 C.) temperature level. This will insure thatproducts of pyrolysis generated above this level move upwardly, whereasthose generated below this level move downwardly. Below this level,i.e., above this temperature, the products of pyrolysis are principallyof lower molecular weight and in such limited amounts as not toseriously contaminate the phosphorus produced.

Whenever a temperature of 1260 C. is obtained in the base 38 of heatingzone 2, the grate bars 39 are started in rotation for the continuousremoval of exhausted charge. Simultaneously fresh charge is suppliedintermittently by operation of bell valves 34 and 36 to maintain anupper level substantially at the line 37. In continuous operation thetemperature at the level of outlets 48 and 49 should be held betweenabout 950 C. and 1050 C. (preferably about 1000 C.) and the rate ofrotation of the grate bars set to provide a residence time of at least 3hours from the 1100 C. level down to the final level of about 1260 C.This will liberate about 95% of the phosphorus content of the ore. Asheretofore explained, the rate of operation of the valve 71 and/or pump72 is set to carry the heavier products of pyrolysis overhead throughoutlets 44 and 45.

In continuous operation the temperature adjacent the outlets 44 and 45should be maintained between about 300-400 C., preferably about 350 C.

Of the products of pyrolysis passing off through main 46, as heretoforedescribed, the tars are knocked down in quench tank 53 by contact withfresh tar introduced through valved pipe 54, and after passing throughcooler 59 are carried 01f to storage through valved pipe 65. Theremaining hydrocarbons passing oif through valved pipe 71 and pump 72into rectifying column 73 are split roughly into two fractions, i.e., anoverhead fraction con sisting principally of benzol and toluol, theexcess of which over that recycled as reflux through line 95 is carriedoff through valved pipe 96, and a bottoms of heavier aromatics carriedoff through valve pipe 77.

I claim:

1. The continuous process of winning phosphorus from oxygenated orescontaining the same which comprises mixing such an ore in particulateform with a carbonizing agent which becomes only plastic and not freelyfluid up to the temperature of pyrolysis, thereby forming a mixture,said mixture containing sufficient carbon-yielding substance to form acoke in which the carbon is in excess over that consumable in thereduction of the P and other reducible oxides present, thereafterbriquetting said mixture, maintaining, a charge of such briquettes in avertically oriented heating zone with provision for top feed and bottomdischarge, heating said charge in the upper portion of said heating zoneout of direct contact with combustion gases to a temperature betweenabout 350-1000 C. for a period of time sufiicient to substantiallycomplete pyrolysis, thereafter further heating said charge in the lowerportion of said heating zone to a temperature of between 950 and 1050 C.at which reduction proceeds with the formation of carbon monoxide andpho'sphorus in gas' phase and until at" least a n'iajtii part of thephosphorus content of said ore has been liberated, adding freshbriquettes to said charge at the upper end thereof and removing residualcarbonand residual ore particles from said heating zone at the lower endthereon-conducting away said carbon monoxide and phosphorus in gas phasefromsaid charge at an intermediate point and separately conducting awaythe heavier products of pyrolysis from said charge at a higher point.

2. Process according to claim 1 in which said carbon monoxide andphosphorus in gas phase are taken off from said charge between about atemperature level of 950- 1050" C.

3. Process according to claim '1 in which said carbon monoxide andphosphorus are taken on from said charge at a temperature level of aboutthe 1000 C.

4. Process according to claim 1 in which said heavier products ofpyrolysis are taken 01f from said charge at a temperature level ofbetween about the BOO-400 C.

5. Process according to claim 1 in which said products of pyrolysis areprincipally taken off from said charge at a temperature level of aboutthe 350 C.

6. Process according to claim 1 in which said carbon monoxide andphosphorus in gas phase are taken off from said charge at a temperaturelevel of between about 9501050 C., and said heavier products ofpyrolysis are taken 01f from said charge at a temperature level of aboutbetween 300400 C.

7. The continuous process of winning phosphorus from oxygenated orescontaining the same, which comprises mixing such an ore in particulateform with a carbonizing agent which becomes only plastic and not freelyfluid up to the temperature of pyrolysis, thereby forming a mixture,said mixture containing sufficient carbonyielding substance to form acoke in which the carbon is in excess over that consumable in thereduction of the P 0 and other reducible oxides present, thereafterbriquetting said mixture, maintaining a charge of such briquettes in avertically oriented heating zone with provision for top feed and bottomdischarge, heating said charge in the upper portion of said heating zoneout of direct contcat with combusion gases, to a temperature betweenabout 350-1000" C. for a period of time sufficient to substantiallycomplete pyrolysis, thereafter further heating said charge in the lowerportion of said heating zone to a temperature of between about 950 and1050 C. at which reduction proceeds with the formation of carbonmonoxide and phosphorus in gas phase and until at least a major part ofthe phosphorus content of said ore has been liberated, adding freshbriquettes to said charge at the upper end thereof and removing residualcarbon and residual ore particles from said heating zone at the lowerend thereof, conducting away said carbon monoxide and phosphorus in gasphase from said charge at an intermediate point and separatelyconducting away the heavier products of pyrolysis from said charge at ahigher point, the rate of flow of said heavier products of pyrolysisbeing established at a rate that produces a maximum pressure in theupper part of said heating zone above the point at which said carbonmonoxide and phosphorus in gas phase are conducted away between the700800 C. temperature levels.

'8. Process according to claim 7 in which said carbon monoxide andphosphorus in gas phase are taken off from iaidlcharge between about the9501050 C. temperature eve s.

9. Process according to claim 7 in which said carbon monoxide andphosphorus are taken oif from said charge at about the 1000 C.temperature level.

10. Process according to claim 7 in which the said heavier products ofpyrolysis are taken off from said charge between about the 300-400 C.temperature levels.

11. Process according to claim 7 in which said products of pyrolysis areprincipally taken off from said charge at about the 350 C. temperaturelevel.

112. Process according to claim 7 in which said carbon monoxide andphosphorus in gas phase are taken off from said charge between about/she95 0-1050 C. temperature 5 levels and said heavier products of pyrolysisare taken ofi from said charge between the 300 400 C. temperaturelevels,

References Cited in the file of 'this patent UNITED STATES PATENTSCurtis Feb. 4, '1936 France June 16, 1930

1. THE CONTINUOUS PROCESS OF WINNING PHOSPHORUS FROM OXYGENATED ORESCONTAINING THE SAME WHICH COMPRISES MIXING SUCH AN ORE IN PARTICLE FORMWITH A CARBONIZING AGENT WHICH BECOMES ONLY PLASTIC AND NOT FREELY FLUIDUP TO THE TEMPERATURE OF PYROLYSIS, THEREBY FORMING A MIXTURE, SAIDMIXTURE CONTAIING SUFFICIENT CARBON-YIELDING SUBSTANCE TO FORM A COKE INWHICH THE CARBON IS IN EXCESS OVER THAT CONSUMABLE IN THE REDUCTION OFTHE P2O5 AND OTHER REDCUCIBLE OXIDES PRESENT, THEREAFTER BRIQUETTINGSAID MIXTURE, MAINTAINING A CHARGE OF SUC BRIQUETTES IN A VERTICALLYORIENTED HEATING ZONE WITH PROVISION FOR TOP FEED AND BOTTOM DISCHARGE,HEATING SAID CHARGE IN THE UPPER PORTION OF SAID HEATING ZONE OUT OFDIRECT CONTACT WITH COMBUSTION GASES TO A TEMPERATUE BETWEEN ABOUT350-1000*C. FOR A PERIOD OF TIME SUFFICIENT TO SUBSTANTIALLY COMPLETEPYROLYSIS, THEREAFTER FURTHER HEATING SAID CHARGE IN THE LOWER PORTIONOF SAID HEATING ZONE TO A TEMPERATURE OF BETWEEN 950 AND 1050*C. ATWHICH REDUCTION PROCEEDS WITH THE FORMATION OF CARBON MONOXIDE ANDPHOSPHORUS IN GAS PHASE AND UNTIL AT LEAST A MAJOR PART OF THEPHOSPHORUS CONTENT OF SAID ORE HAS BEEN LIBERATED, ADDING FRESHBRIQUETTES TO SAID CHARGE AT THE UPPER END THEREOF AND REMOVING RESIDUALCARBON AND RESIDUAL ORE PARTICLES FROM SAID HEATING ZONE AT THE LOWEREND THEREOF, CONDUCTING AWAY SAID CHARGE AT AN AND PHOSPHORUS IN GASPHASE FROM SAID CHARGE AT AN INTERMEDIATE POINT AND SEPARATELY CONDUCINGAWAY THE HEAVIER PRODUCTS OF PYROLYSIS FROM SAID CHARGE AT A HIGHERPOINT.